Re: [RFC][PATCH 3/6] x86/topo: Add __num_nodes_per_package

[Kyle Meyer]

On Thu, Feb 26, 2026 at 11:49:12AM +0100, Peter Zijlstra wrote:
> Use the MADT and SRAT table data to compute __num_nodes_per_package.
> 
> This number is useful to divinate the various Intel CoD/SNC modes,
> since the platforms are failing to provide this otherwise.
> 
> Doing it this way is independent of the number of online CPUs and
> other such shenanigans.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/topology.h |    1 +
>  arch/x86/kernel/cpu/common.c    |    3 +++
>  arch/x86/kernel/cpu/topology.c  |    9 ++++++++-
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -158,6 +158,7 @@ extern unsigned int __max_logical_packag
>  extern unsigned int __max_threads_per_core;
>  extern unsigned int __num_threads_per_package;
>  extern unsigned int __num_cores_per_package;
> +extern unsigned int __num_nodes_per_package;
>  
>  const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
>  enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c);
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -95,6 +95,9 @@ EXPORT_SYMBOL(__max_dies_per_package);
>  unsigned int __max_logical_packages __ro_after_init = 1;
>  EXPORT_SYMBOL(__max_logical_packages);
>  
> +unsigned int __num_nodes_per_package __ro_after_init = 1;
> +EXPORT_SYMBOL(__num_nodes_per_package);
> +
>  unsigned int __num_cores_per_package __ro_after_init = 1;
>  EXPORT_SYMBOL(__num_cores_per_package);
>  
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -497,11 +497,18 @@ void __init topology_init_possible_cpus(
>  	set_nr_cpu_ids(allowed);
>  
>  	cnta = domain_weight(TOPO_PKG_DOMAIN);
> +	cntb = domain_weight(TOPO_NUMA_DOMAIN);

We'll need to check CONFIG_NUMA here.

TOPO_NUMA_DOMAIN is undeclared when CONFIG_NUMA is not set.

> +
> +	__num_nodes_per_package = DIV_ROUND_UP(cntb, cnta);
> +
> +	pr_info("Max. logical packages: %3u\n", cnta);
> +	pr_info("Max. logical nodes:    %3u\n", cntb);
> +	pr_info("Num. nodes per package:%3u\n", __num_nodes_per_package);
> +
>  	cntb = domain_weight(TOPO_DIE_DOMAIN);
>  	__max_logical_packages = cnta;
>  	__max_dies_per_package = 1U << (get_count_order(cntb) - get_count_order(cnta));
>  
> -	pr_info("Max. logical packages: %3u\n", cnta);
>  	pr_info("Max. logical dies:     %3u\n", cntb);
>  	pr_info("Max. dies per package: %3u\n", __max_dies_per_package);
>  
> 
>